1. Field of the Invention
The invention relates generally to devices for sharpening band saws used in the lumber industry and for sharpening saws used in other industrial and commercial applications. More specifically, the invention pertains to a computer-controlled system, for driving the saw blade advancing and saw blade grinding components of a saw sharpener.
2. Description of the Prior Art
Automatic band saw sharpeners have been available for many years. These sharpeners are used to sharpen large, industrial ban saws, used primarily in the lumber industry. Typically, such sharpeners include a main sharpener frame and a plurality of outboard support posts. These posts maintain the blade in a horizontal, oval-like configuration during the sharpening operation. Prior art sharpeners employ a feed finger mechanism to index the band saw in sequential, stepped fashion through the sharpener, while the grinding wheel of a grinding head assembly is successively lowered into and raised from the blade to shape each tooth.
Cam-actuated mechanism have previously been used to drive both the feed finger and the grinding head in the proper timed relationship. For example, in the prior art band saw sharpener manufactured by the Armstrong Manufacturing Company of Portland, Oreg., an electric motor rotates a drive shaft upon which at least two separate cams are located. A treadle arm, connected to the grinding head assembly, includes a cam follower on its lower end for engagement with one of the cams. In similar fashion, a feed finger arm is connected to the feed finger mechanism, and includes a cam follower on its lower end for engagement with the other cam. Rotating the drive shaft effects X-axis movement of the feed finger and Y-axis movement of the grinding head assembly, so as to grind the desired tooth configuration into the saw.
If single lobe drive cams are used, such a sharpener will produce teeth having the same pitch and the same gullet depth. However, it has been determined that variable tooth patterns in the saw may be desirable, as certain operational advantages are provided. For example: the feed speeds for sawing the subject lumber may be increased; the xe2x80x9cwashboardxe2x80x9d pattern that same pitch and same depth teeth impress in the lumber may be eliminated or reduced; and, the size of the kerf produced in the cut lumber may also be reduced, saving wood product.
To satisfy this need, prior art sharpeners were developed which use drive cams having multiple lobes to produce variable pitch and variable depth gullets. It has also been advocated to provide up to three pairs of such cams on a single drive shaft, so that different pitches and different gullet depths may appropriately be selected for the particular saw to be sharpened. However, it is time consuming to move and relocate the cams and then set up the sharpener so it is adjusted properly for the different grinding operation. Moreover, a considerable investment must be made to acquire and maintain the cams corresponding to each selected pitch and depth.
Another disadvantage of the cam-actuated system is the mechanical wear that results from long-term use of the sharpener. Mechanical wear in drive components, such as the drive cams and the cam followers, can cause improper and erratic grinding patterns, resulting in undesirable tooth size and shape. In addition, replacing the cams is expensive, and results in down time for the sharpener.
In recognition of these disadvantages, efforts have been made to redesign or replace the cam-actuated mechanisms in saw sharpeners. Specifically, a number of patents have issued for more modern saw blade sharpeners, some of which incorporate programmable computers or controllers. Other sharpeners disclosed in recently issued patents employ alternative drive mechanisms for their saw blade driving and grinding head components.
For example, U.S. Pat. No. 5,488,884, issued to Andrianoff et al., shows an apparatus for side-grinding saw blade teeth. This apparatus uses a commercially available programmable controller, and includes pneumatic cylinders to move the grinding head assembly. In U.S. Pat. No. 5,471,897, granted to Wright, a xe2x80x9cconventional computer numeric controllerxe2x80x9d is used to provide sharpening functions. The Wright reference also shows the use of servo motors and ball screw mechanisms, to effect movement of the grinding wheel assembly, in the X and Y axes. And, in U.S. Pat. No. 5,826,465, issued to Iseli, a band saw manufacturing method is disclosed which uses hydraulic rams for advancing and retracting the xe2x80x9cgrinding wheel arrangementxe2x80x9d.
Nevertheless, the need exists for an apparatus which may be installed as a retrofit to a prior art cam-actuated sharpener, giving it vastly improved flexibility and performance: and, the need further exists for economical drive and control systems which may be incorporated into new saw sharpeners, which systems provide reliability and accuracy not attainable by known prior art devices.
The present invention uses a programmable computerized controller, for actuating both an X-axis driver and a Y-axis driver. Each of these drivers employs a rotatable ball screw, a non-rotatable ball screw nut in threaded engagement with the ball screw, a reciprocating carrier box for the screw nut, a servomotor driving one end of the ball screw, an encoder to provide feedback information to the controller regarding the rotational position of the servomotor, and a micro switch positioned to actuate at a predetermined xe2x80x9chomexe2x80x9d location for the carrier box for the ball screw nut.
If the invention is implemented as a retrofit conversion to a prior art band saw sharpener, the drivers replace an existing motor driven cam mechanism. This mechanism typically includes an electric motor driving a shaft provided with two cams. The cams are engaged by respective cam followers, connected to respective drive arms. One drive arm moves a saw feed mechanism in a horizontal, or X-axis direction, and the other drive arm moves a grinding head mechanism in a vertical, or Y-axis direction. The coordinated horizontal movement of the saw blade and the vertical movement of the grinding head, effect grinding of the desired saw tooth shape in the blade.
To install the present invention as a retrofit conversion, the electric motor for driving the cam shaft, the shaft, the cams, the bearings supporting the shaft, and the cam followers, are all removed. A sub-frame, including parallel shafts strategically located to support each of the new X-axis and Y-axis drivers, is then installed. The sub-frame is conveniently installed to the main frame using the same holes used to secure the just-removed cam shaft bearings. The carrier box of each driver is bolt-connected directly to a foot or an end of the existing drive arms in the same place where the cam followers were previously attached.
The computerized controller is mounted to the sharpener frame, and cables extending therefrom provide electrical interconnections to each of the drivers. The controller appropriately actuates the driver servo motors, which in turn effects rotation of the ball screws, resulting in reciprocating X and Y axis movement of the drive arms. In this manner, the retrofit drivers control the saw blade feed and grinding head components just like the prior art cam-driven mechanisms did.
However, because the computerized controller is programmable, virtually any tooth shape can be produced by the sharpener without changing any of its mechanical components. For example, the controller can effect standard-tooth profiles, variable-pitch tooth profiles, and variable depth tooth profiles. The controller may be switched from one tooth profile to another in seconds, merely by touching a button. The controller has two grinding modes for each tooth profile, a standard grind and a retip grind. In the retip grinding mode, the grinding feed rate is slowed down while the top and the face of the new tip are shaped, and then the normal grinding speed is resumed while shaping the remainder of the tooth profile.
If the invention is implemented as part of a new band saw sharpener construction, substantially the same components are used, except the entire electric motor, shaft, cams, and cam follower components of the prior art device are never used or installed, resulting in substantial savings.
Therefore, it is an object of the present invention to provide a computer-controlled band saw sharpener, which may be implemented either as a retrofit modification to an old sharpener, or as part of a newly constructed sharpener, and which can grind standard-tooth profiles, variable-pitch profiles, and variable depth profiles, without changing any mechanical components.
It is a further object herein to disclose an electronically actuated X-axis driver and a Y-axis driver, each employing a servo motor, a rotatable ball screw, and a non-rotatable ball nut for improved accuracy, flexibility, and control over the operation of a feed finger mechanism and a grinding head assembly in a saw sharpener.
It is yet a further object herein to disclose a computer-controlled driver for use with a sharpener, in which the driver includes a rotatable ball screw driving a ball nut fixed within a movable carrier box, in which the carrier box is supported entirely by the ball nut and captive balls.
It is yet a further object herein to disclose a computerized controller for electronically actuated X and Y axis drivers in a saw sharpener, which controller is programmable to effect a wide variety of different pitch and gullet depths for saw teeth, by a button selection made by the user.
It is yet a further object herein to disclose a lever actuated lifting mechanism, for raising the grinding head assembly of a saw sharpener into a disabled position, above the saw.